The present invention relates to apparatus for simultaneously measuring the visual field perimeter and psychomotor tracking performance of a human subject, and more particularly to apparatus for measuring human tolerance as a function of visual field perimetry and psychomotor tracking performance at different levels of acceleration (G).
When a human subject is exposed to high vertical upward or "eyeballs down" acceleration (G.sub.z), blood supply to the eyes and brain is reduced due to increased loading of the heart-brain hemodynamic column. Progressive reduction of blood flow results in a dimming of vision or "gray-out", a narrowing of the visual field, a total loss of vision or "black-out", and ultimately a loss of consciousness. Because intraocular pressures exceed intracranial pressures, blood flow to the eyes is interrupted before blood flow to the brain, and loss of vision generally precedes loss of consciousness. In addition to the hemodynamic effects, exposure to increased G.sub.z -forces degrades psychomotor tracking performance. By measuring the extent and rate of narrowing of the visual field perimeter and the psychomotor tracking ability of a subject, it is possible to establish an end point for tolerance to G.sub.z -forces.
Prior art devices have been found unsuitable for this particular purpose. In general, the response parameters used for determining acceleration tolerance are not related to the natural and instinctive movements of the subject. They require extensive training and physical endurance. Most devices also use white incandescent lamps generating light in a spectral range which is too easily detected by the retinal receptors (rods), and which is transiently visible after the lamps have been deenergized. One device assesses G-tolerance with a linear array of white lights spaced along an arcuate bar subtending a viewing angle on each side of a central red light. Opposite lights are electrically connected in pairs and sequentially illuminated inwardly or outwardly at a fixed rate. The direction is reversed by operation of a hand-operated push button. The G-tolerance of the subject is assessed by his ability to maintain the light pairs illuminated near the edge of his useful vision. This system is susceptible to "cheating" because a skillful subject could deceptively operate the push button at a rate which would maintain a constant light position, even though his peripheral vision has been reduced to where the light is not visible. In addition, this device cannot measure psychomotor tracking performance because the rate at which the illumination moves in or out remains constant.
Another system involves a lamp randomly illuminated and located in the subject's visual periphery. When the lamp is illuminated, the subject immediately presses a button to extinguish it. If he does not respond within a few seconds, the subject is considered not to have seen the lamp, and his vision is regarded as impaired. The limits of the subject's visual field and the rate at which it collapses are not measured. In addition, there is no measure of visual functioning except at the discrete points in time when the lamp is illuminated, and no indication of psychomotor tracking ability.